Liquid pressure bulge forming apparatus

ABSTRACT

A pipe to be formed is placed into a die having a cavity corresponding to the form desired. High pressure liquid is introduced into the pipe, while both ends thereof are compressed thus bulging the pipe, without heating it, in the die cavity to the form desired.

United States Patent Ueda et a]. 51 A r. 11 1972 [54] LIQUID PRESSURE BULGE FORMING 1 References Cited APPARATUS UNITED STATES PATENTS [721 1mm: 19119; m: i 3,350,905 11/1967 Takashi Ogura m1 ..72/62 1,530,000 3/1925 Kaufi'man ...72/351 [73] Assignee: Agency of lndustriaiScience 8: Technolo- 3,072,085 l/1963 Landis ..72/62 gy,T y p 3,335,590 8/1967 Early ..72/62 3,358,488 l2/l967 Fuchs, Jr. ..72/62 221 F1led. Jan. 27, 1970 [211 6,258 Primary Examiner-Richard J. Herbst Attorney-Emest G. Montague 301 Foreign Application Priority um Jan. 29, 1969 Japan ..44/65l6 [571 ABSTRACT A pipe to be formed is placed into a die having a cavity corc l. ..72/2s,72 6 1 29g 1 responding to the form desired. High pressure liquid is u I I I 8 I I l l I I I u u n v n 5 l l u 5 u I u [58] FieldofSearch ..72/57,58,60,6l,62,28 pressed thus bulging the pipe without heating it in the die cavity to the form desired.

4Claims,4Drawing 44 28 43 3 40 05 54.15 a J4 4.9 22 18 r-m 9 15 12 12' 91 ,3?

LIQUID PRESSURE BULGE FORMING APPARATUS The present invention relates to a liquid pressure bulge forming apparatus for a metal working process. More particularly, it relates to an apparatus for bulge forming pipe wherein the part of the pipe to the processed can be bulged to the form desired by conducting a high pressure liquid thereinto.

One of the present inventors cooperated in the development of the liquid pressure bulge forming apparatus describe in U.S. Pat. No. 3,350,905. The present invention, which is a further improvement of the prior art, provides a novel bulge forming apparatus of simpler construction with which machinery parts such as T-joints, expandable corrugated pipe, head lugs and seat lugs for bicycles, etc., can be efficiently produced at a low cost.

It is the main object of the present invention to provide a bulge forming apparatus which permits easy interchange of dies having cavities of various shape and thus permits bulging of the pipe to any form desired.

It is still another object of the present invention to provide an apparatus wherein the sealing pressure which prevents the break in the seal between said pipe and piston rods can be steplessly regulated in accordance with the change in the diameter of a pipe to be formed.

It is another object of the present invention to provide an apparatus in which a pipe having different diameters at both ends can be said satisfactorily bulged.

It is another object of the present invention to provide an apparatus whereby bulging work can be carried on while maintaining a very high degree of safety.

Other objects and features of the present invention will become apparent in the following detailed description takes in conjunction with the accompanying drawings, in which:

FIG. 1 is a front view, partly in section, of an apparatus incorporating the oil pressure piping system of the present invention;

FIG. 2 is a side view of the above apparatus;

FIG. 3 is a perspective view of a die for forming corrugated pipes; and

FIG. 4 is a piping diagram for the continuously variable pressure regulator in accordance with the present invention.

Referring to FIG. 1, metal pipe 1 cut to a proper length and having a polished surface is placed in lower die 2 fixed to frame 13. Upper split die 2 fixed to piston 3 is then pressed down on die 2.

In the embodiment shown in FIG. 1, the split die has only one die cavity 15. A plurality of die cavities, however, can be provided, if they are the same in diameter. These cavities can further be formed as shown in FIG. 3 to make a die for the production of expandable corrugated pipe.

By introducing liquid pressure into pressure cylinder 19, rigidly fixed to frame 13, from pump 16 through check valve 17, pressure piston 20 is moved downwardly to cause a cam located at the end of the piston to move down. Roller bearings and 10 are provided at the lower end of links 7 and 7 connected to frame 13 by pins 8 and 8 so that the roller bearings contact inclined surfaces 12 and 12' of cam 11. With the downward movement of cam 11, the roller bearings are pushed outward. Therefore, links 7 and 7' rotate around pins 8 and 8 and the upper ends thereof are pushed inwardly. Connecting rods 6 and 6 connected to the upper portions of links 7 and 7 by pins 9 and 9' are driven toward the center and piston rods 4 and 4' connected to the ends of the connecting rods 6 and 6' seal both ends of the pipe 1.

The pressure applied for sealing both ends of the pipe by piston rods 4 and 4' should be such that the pressure at the contact surfaces of the pipe 1 with piston rods 4 and 4' is higher than the pressure of the liquid introduced into pipe 1. At the same time, such pressure should be controlled so that the pipe is not axially deformed by excessive pressure. If the pipe is axially deformed at this step, the pipe will undergo work hardening which hinders proper bulge formation.

Liquid is supplied from low-pressure pump 26 through check valve 27, high pressure piping 25, high pressure connecting cylinder 5 fixed to frame 13 and high pressure liquid passage 29' within connecting rod 6' into and filling pipe 1 so that any existing air within pipe 1 is forced out through high pressure liquid passage 29 within connecting rod 6, high pressure connecting cylinder 5 fixed to frame 13, and high pressure pilot check valve 28 thus completely replacing the air by the liquid.

Next, liquid having pressure high enough to bulge pipe 1 is introduced into the pipe from pump 21 through pressure intensifier 22. The high pressure liquid acts on the end surfaces of piston rods 4 and 4, which are pushed outwardly by the force of the high pressure liquid. The link mechanism is then moved to cause pressure piston 20 to be pushed upwardly. As a result of this movement of the pressure piston, the seal between the ends of pipe 1 and the end portions of piston rods 4 and 4 is broken. In order to prevent breaking of the seal, a device called a reaction offset means is provided. This reaction ofiset is effected by utilizing continuously variable pressure regulator 36 which as shown in FIG. 4 comprises lever 37, pressure ratio changing cylinder 32, buffer cylinder 39 and relief valve 38.

Thus pressure ratio changing cylinder 32 can be set at a position along the side surface of lever 37 thereby determining the pushing force applied to relief valve 38 through buffer cylinder 39 and making it possible for the continuously variable pressure regulator to control the relationship between pressure P in the piping system for generating high pressure liquid by means of pump 21 and pressure I, in the piping system for reaction offset generated by pump 31 in accordance with the equation P m-P (where m is a parameter determined by the diameter of the pipe to be bulged). The reaction force generated by the high pressure liquid introduced into pipe 1 is higher at the time of processing a pipe of large diameter than at the time of processing a pipe of small diameter, and the pushing force of pressure piston 20 due to the reaction force becomes higher. Accordingly, in order to prevent breaking of the seal, cylinder 32 should be moved to a position closer to relief valve 38 as the diameter of the pipe becomes larger, thus increasing the pressure generated by pump 31 and applied on pressure piston 20. That is, an appropriate parameter m is selected by changing the position of cylinder 32 in accordance with the diameter of the pipe to be formed. Thus, the pressure P in the piping system for generating high pressure liquid and the pushing force of pressure piston 20, namely, pressure P; in the piping system for reaction ofiset are maintained in a proportional relation, whereby breaking of the seal is prevented.

Now, if the high pressure liquid is introduced into pipe I, pipe 1 gradually deforms within die cavity 15 forming a semespherical bulged portion. Then, liquid pressure is introduced into pressure cylinder 19 from pump 16 and pressure piston 20 is moved downwardly by applying a liquid pressure higher than the liquid pressure applied at the time of sealing the ends of pipe 1. Thus, both ends of pipe 1 are compressed by means of the link mechanism in an axial direction simultaneously at the same speed and pipe 1 can thus be satisfactorily formed within die cavity 15, without being heated, by means of the high pressure liquid in pipe 1 in conjunction with the compression force. In the bulge forming process, the liquid pressure in pipe 1 and in the high pressure liquid passage naturally increases in accordance with the difference between the volume of the bulge portion and the volume decrease of the straight portion of the pipe caused by the axial compression. If such pressure increases over a certain value, the bulge portion will be destroyed. Accordingly, it is necessary to regulate the aforementioned pressure increase within limits depending upon the size, quality etc, of the pipe to be formed. In order to regulate the pressure, pressure regulating valve 33 and pressure regulating cam 41 are provided. Cam 41 is connected with the rear end of the connecting rod 6' and has inclined surface 42 having a specific relation between the compressive length of pipe 1 and the liquid pressure in pipe 1. Follower wheel 40 contacts inclined surface 42 and operates pressure regulating valve 33 so that the pressure in pump 21, that is, the

pressure on the primary side 23 of pressure intensifier 22 is properly controlled. Consequently, the high liquid pressure generated within pipe 1, that is, the pressure on the secondary side 24 of pressure intensifier 22, can be thus regulated. Through the above-mentioned control of the high pressure liquid, pipe 1 is properly bulged within die cavity without causing damage to the bulged portion.

After the completion of this bulge forming process, the product is removed. Pressure piston is raised by conducting the liquid pressure produced by pump 16 to lower portion 18 of pressure cylinder 19. Roller bearings 10 and 10' are pressed onto inclined surfaces 12 and 12' of cam 11 by means of return brackets 14 and 14' projecting from cam 11 which is rigidly fixed to piston 20 and the upper portions of link 7 and 7 are moved outwardly thus moving piston rods 4 and 4 outwardly. Simultaneously, knock-out piston 34 is operated by the liquid pressure supplied by pump 35 after upper die 2 is elevated, such elevation being effected by liquid pressure from pump 43 to the lower inlet of die clamping cylinder 44. The product can then be removed from lower die 2'.

In the embodiment described in the present specification, the shape of cam 11 is of symmetrical shape and the pipe is compressed an equal length on both ends. The bulge formation on a pipe having different diameters at both ends thereof, however, can be easily achieved by making the inclined surfaces of said links unsymmetrical in accordance with the difference in the diameters of the ends of the pipe to be processed and thus making degree of compression different at each end.

In addition, guide plates 13 serving also as space plates on frame 13 are provided at the lower portions of the cam. Pressure indicators are provided at the sides where these guide plates face with each other. Pressure indicators 30 indicate any unbalance in the links moving downwardly. When indicators 30 detect over a predetermined degree of pressure the machine is automatically shut down and the safety of the apparatus is thus always maintained.

Through use of the continuously variable pressure regulator of the present invention, the counter pressure generated by the high pressure liquid in the pipe which is inclined to break the seal between the pipe and the piston rods can be steplessly counteracted, and products of various shape can therefore be easily formed and produced. Also, the the link mechanism of the present invention is of more simple construction than the conventional mechanism. Further, if both sides of the cam of the link mechanism are formed to have an inclination corresponding to the pressure force respectively exerted at the pipe ends, a pipe having different diameters at both ends thereof can be easily formed.

What we claim is:

l. A liquid bulge forming apparatus, comprising a die comprising a plurality of members with cavities of various shapes which hold a pipe to be formed therein and permit bulging of said pipe to a desired form,

a pair of reciprocable piston rods aligned in an opposing arrangement sealingly holding said pipe therebetween.

means for conducting a high pressure liquid into said pipe constituting a bulge forming operation,

a stepless and continuously variable reaction offset means for preventing a break of the seal between said piston rods and said pipe when introducing said high pressure liquid into said pipe,

at pressure regulating means for controlling a pressure for preventing rupture of said pipe due to said high pressure liquid during the bulge forming process,

a safety means responsive to the pressure in said pipe and for shutting down said apparatus when said pressure exceeds predetermined pressures, and

means operatively connected to said reaction offset means for causing said piston rods, respectively, to move forward each at predetermined speeds thereby pressing said pipe during said bulge forming operation.

2. The apparatus, asset forth in claim 1, wherein said means for causing said pair of piston rods to move forward comprises,

a pressure piston,

a cam rigidly fixed to the lower portion of said pressure piston,

pivotally mounted links slidable along side portions of said cam,

connecting rods connected to upper portions of said links and to said piston rods, said side portions of said cam are each formed such that said piston rods, respectively are moved forward each at said predetermined speeds by means of a downward movement of said pressure piston.

3. The apparatus, as set forth in claim 1, wherein said reaction offset means constitutes a continuously variable pressure regulator comprising, a one-armed lever,

a relief valve, a buffer cylinder connecting one end of said lever with said relief valve, and

a pressure ratio changing cylinder freely settable at any position along the surface of said lever wherein the position at which said pressure ratio changing cylinder is set determines the ratio between the pressure for forming the bulge and the pressure operatively applied to said means for causing said piston rods to move forward.

4. The apparatus, as set forth in claim 1, further comprising a frame,

said safety means comprises,

guide plates facing each other and mounted on said frame adjacent the lower portions of said cam, and

pressure indicator means disposed at the sides of said guide plates where the latter face each other and for detecting pressures over predetermined pressures and for shutting down said apparatus thereupon. 

1. A liquid bulge forming apparatus, comprising a die comprising a plurality of members with cavities of various shapes which hold a pipe to be formed therein and permit bulging of said pipe to a desired form, a pair of reciprocable piston rods aligned in an opposing arrangement sealingly holding said pipe therebetween. means for conducting a high pressure liquid into said pipe constituting a bulge forming operation, a stepless and continuously variable reaction offset means for preventing a break of the seal between said piston rods and said pipe when introducing said high pressure liquid into said pipe, a pressure regulating means for controlling a pressure for preventing rupture of said pipe due to said high pressure liquid during the bulge forming process, a safety means responsive to the pressure in said pipe and for shutting down said apparatus when said pressure exceeds predetermined pressures, and means operatively connected to said reaction offset means for causing said piston rods, respectively, to move forward each at predetermined speeds thereby pressing said pipe during said bulge forming operation.
 2. The apparatus, as set forth in claim 1, wherein said means for causing said pair of piston rods to move forward comprises, a pressure piston, a cam rigidly fixed to the lower portion of said pressure piston, pivotally mounted links slidable along side portions of said cam, connecting rods connected to upper portions of said links and to said piston rods, said side portions of said cam are each formed such that said piston rods, respectively are moved forward each at said predetermined speeds by means of a downward movement of said pressure piston.
 3. The apparatus, as set forth in claim 1, wherein said reaction offset means constitutes a continuously variable pressure regulator comprising, a one-armed lever, a relief valve, a buffer cylinder connecting one end of said lever with said relief valve, and a pressure ratio changing cylinder freely settable at any position along the surface of said lever wherein the position at which said pressure ratio changing cylinder is set determines the ratio between the pressure for forming the bulge and the pressure operatively applied to said means for causing said piston rods to move forward.
 4. The apparatus, as set forth in claim 1, further comprising a frame, said safety means comprises, guide plates facing each other and mounted on said frame adjacent the lower portions of said cam, and pressure indicator means disposed at the sides of said guide plates where the latter face each other and for detecting pressures over predetermined pressures and for shutting down said apparatus thereupon. 